Movement devices associated with elements of furniture such as chairs, stools, swivel armchairs, in order to allow the movement of their seat in a preselected position with respect to a fixed portion are known.
Known devices typically comprise a shaft which is fixed to a lower surface of the seat of a chair and a hub which is fixed to a pedestal part of the chair. A lower part of the shaft is connected rotatably to the hub, allowing therefore the rotation of the seat with respect to the pedestal.
Substantially two types of movement devices are known, i. e., a first self-aligning type, which is configured to return the seat automatically to a preset angular position at the end of the use of the chair, and a second freely rotating type, which is shaped in order to allow the free rotation of the seat with respect to the fixed portion without automatic return.
In the first known type of movement device, the shaft is elastically countered by a spring, for example a helical spring, arranged inside the hub. The spring is designed to act between an inner surface of the hub and a surface of an annular rim of the shaft.
These known devices have a cam-like kinematic coupling between the shaft and the hub, so that when the seat, and thus the shaft, is rotated with respect to the preset position, due to the cam-like kinematic coupling, an axial sliding of the shaft with respect to the hub is produced between a preset and aligned position and a lowered position.
This axial sliding occurs so as to compress said spring.
When the seat is released, the spring extends, pushing against the second surface of the shaft, and due to the cam-like kinematic coupling produces the lifting and rotation of the shaft, therefore of the seat, from the lowered position to the preset position, allowing to self-align automatically said seat in its preset position.
With this known device, the spring constantly exerts its elastic thrust against the surface of the shaft, producing a constant torque on the shaft, which affects the seat in a substantially equivalent manner.
Therefore, the user undergoes a rotation, albeit minimal, which is induced by the seat and in order to maintain the preselected angular position has to contrast this rotation by muscular action with his pelvis and lumbar region.
With these known devices there is, moreover, the tendency, due again to the action of the spring, to have uncontrolled and unintentional rotations of the seat during its use.
In the second type of known devices, the rotation of the shaft with respect to the hub, and therefore of the seat with respect to the pedestal, is completely free, allowing uncontrolled and unintentional rotations of the seat during its use, for example due to the inertias generated by the movements of the user's arms.
In this known solution, the user is often forced to counter these rotations with his pelvis and lumbar region in order to return to the preselected angular position.
In both of said known solutions, the muscular contrast that is needed involves, in the long run, a tiring and stiffening of the muscles involved, with consequent aching and discomfort in sitting.
For these reasons, these type of known seats has a limited application, particularly in the case of applications in which is necessary to provide ample comfort to the user, even for long periods of use, such as for example in the field of gaming machines and equipment, work and entertainment stations, or others.
Moreover, chairs provided with the known devices are not adjustable in height by virtue of specific adjustment devices which are independent and separate with respect to the movement device. This entails an increase in the manufacturing costs and functional complexity of installation.
The aim of the present invention is to provide a movement device for an element of furniture, such as a chair, a stool, an armchair or others, that allows to maintain a high stability of the seat during its normal use without requiring the user to perform the necessary and different contrast rotations required to restore or maintain the preselected position.
JP 7 222637 A describes a direction restoring apparatus for a chair with a stopper 52 to limit the downward movement of a shaft rod 5 supporting the chair, the stopper 52 abutting against the external plane surface of a fixed cam member 4 disposed to close the top end of a cylindrical support leg pipe 1 of the chair. Further, according to JP 7 222637 A, a jutting element 6 is disposed on the rod shaft 5 and within the cylindrical support leg pipe 1 to guide the rotational upward movement of the shaft rod 5 against the biasing effect of a spring 3 disposed within the cylindrical support leg pipe 1. The guiding of the rotational upward movement is achieved by the interaction between the jutting element 6 and the lower inclined surface of the fixed cam member 4.
Another object of the present invention is to provide a movement device that also allows adjusting the position of the revolving seat in terms of height.
In order to obviate the drawbacks of the background art and achieve these and further objects and advantages, the Applicant has studied, tested and developed the present invention.